There are known coupling assemblies for transmitting torque between a first part and a second part, each of said parts being rotatable with respect to one another. A coupling assembly of this type is described in German Patent No. P 43 43 307 C2, and is sold by the assignee of the present application under the trademark VISCO-LOK.TM..
Such a coupling assembly, which may be referred to as a locking or limited-slip differential device, has various practical applications. A first application is in a differential drive to provide a self-inhibiting or self-locking effect. Such differential drives may constitute axle differentials or central differentials in automotive vehicles.
A second application of a coupling assembly of this type is in the drive train of automotive vehicles having one permanently-driven axle and one axle which is selectively driven only when the coupling assembly is closed, with the coupling assembly being connected between two portions of a shaft linking the source of automotive power to the selectively-driven axle. If a speed differential occurs between the permanently-driven axle and the selectively-driven axle, the coupling assembly is closed to exert torque on the selectively-driven axle. If no speed differential exists between the permanently-driven axle and the selectively-driven axle, the coupling assembly is opened to render the selectively-driven axle free-wheeling.
The reaction behavior of the coupling assembly and the achievable pressure values in the pressure chamber are determined by geometry, particularly by the width and depth of the shear channel. With a predetermined coupling assembly diameter, the width of the shear channel is particularly limited. Although pressure generation may be very effective, and the piston able to apply high forces to the friction coupling, there are applications wherein a more rapid reaction and/or the application of even higher forces to the piston are/is essential, even at small speed differentials.
The present applicants have addressed this need, and have designed a coupling assembly that exhibits such increased performance characteristics without the need for an assembly of undesirably large axial and radial dimensions.